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MergeSort.java

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// Program that implements Merge sort

// Best case: O(nlogn)

// Average case: O(nlogn)

// Worst case: O(nlogn)

public class MergeSortMain {

static int arr[]={100,20,15,30,5,75,40};

public static void main(String args[])

{

System.out.println("Array before sorting:");

printArray(arr,0,arr.length-1);

System.out.println("-----------------------------");

mergeSort(0,arr.length-1);

System.out.println("-----------------------------");

System.out.println("Array After sorting:");

printArray(arr,0,arr.length-1);

}

public static void mergeSort(int start,int end)

{

int mid=(start+end)/2;

if(start<end)

{

mergeSort(start,mid);

mergeSort(mid+1,end);

merge(start,mid,end);

}

private static void merge(int start, int mid, int end) {

int[] tempArray=new int[arr.length];

int tempArrayIndex=start;

System.out.print("Before Merging: ");

printArray(arr,start,end);

int startIndex=start;

int midIndex=mid+1;

while(startIndex<=mid && midIndex<=end)

{

if(arr[startIndex]< arr[midIndex])

{

tempArray[tempArrayIndex++]=arr[startIndex++];

}

else

{

tempArray[tempArrayIndex++]=arr[midIndex++];

}

while(startIndex<=mid)

{

tempArray[tempArrayIndex++]=arr[startIndex++];

}

while(midIndex<=end)

{

tempArray[tempArrayIndex++]=arr[midIndex++];

}

for (int i = start; i <=end; i++) {

arr[i]=tempArray[i];

}

System.out.print("After merging: ");

printArray(tempArray,start,end);

System.out.println();

}

public static void printArray(int arr[],int start,int end)

{

for (int i = start; i <=end; i++) {

System.out.print(arr[i]+" ");

}

System.out.println();

}